1. Field of the Invention
This invention relates to the field of electrocardiography and, more specifically, to a method and apparatus for increasing the throughput and lowering the cost in the process of analyzing ambulatory recorded electrocardiographic (Holter ECG) data by automatically scanning patient recordings at high speed and automatically segregating recordings that contain no significant abnormalities from those that contain significant abnormalities. In the case where a Holter recording has significant abnormalities, the invention terminates the automatic analysis based on preset or variable parameters relative to heart arrhythmias, heart morphology, artifact and a level of confidence provided by special algorithms. The preset or variable parameters relative to heart arrhythmias and heart morphologies are based in part on an expanded Lown grade scale. If the high speed analysis indicates that the preset thresholds are exceeded, then the high speed scan is terminated and the recording is relegated to a manual confirm scan using conventional Holter analysis techniques.
The process above can be represented by a medical term known as "Triage.TM.." Triage.TM. relates to the medical screening of three types of patients to determine their priority for treatment. In the case of the invention, the scanning of Holter tapes involves three operational modes which operate in sequence but in any sequential order. In this case, the three modes are the fully automatic, manual confirm and the new mode known as Triage.TM.. In the Triage.TM. mode where the high speed analysis of a Holter recording can continue automatically where no morphology limits are exceeded, or converts to a manual confirm mode when limits are exceeded, or is terminated early when the recording quality or morphology indicates special manual analysis will be required from the beginning.
2. Description of the Prior Art
In ambulatory monitoring, as normally practiced, the patient wears a device for measuring or sensing physiological or physical variables such as ECG, blood pressure, EEG, posture, etc. These sensed signals are recorded typically on magnetic tape or a solid-state memory. In the case of ECG signals recorded on tape, this is known as a Holter recorder. The recording sessions may last for twenty-four hours or more; thus, the analysis of these tapes is only practical at a higher speed than the recording time, typically 120 to 240 times faster. The signals after analysis on the playback apparatus are typically printed on a high speed laser printer which produces a numerical report with graphical charts and ECG presentations.
Recent developments in high-speed, low-cost computers using Digital Signal Processing (DSP) techniques have made it possible to automatically scan recorded multichannel electrocardiographic data at speeds in the range of 240 to 500 times or higher than the speed at which the data was actually recorded. However, it has remained necessary for most clinical reporting thereon to have skilled personnel scan a tape at high speed, beat by beat, using visual prospective or retrospective techniques to access and correct the computer analyzed data. Using these manual techniques, it is found that typically 30% of the recordings contain no significant abnormalities or artifact; thus, fully automatic analysis is practical with this type of ECG data. The separation of these tapes from the other 70% decreases the amount of skilled technician time in that 30% of the tapes may undergo fully automatic analysis. There still remains the need for scanning recorded ECG data interactively with the technician on a beat-by-beat basis using existing techniques.
An early example of a system for recording and playing back ECG signals is found in Holter et al U.S. Pat. No. 3,215,136 issued on Nov. 2, 1965. A contemporary apparatus for playback and analysis of recorded tapes is described in Cherry and Anderson U.S. Pat. No. 4,006,737 issued Feb. 8, 1977, for "Electrocardiographic Computer." A reissue application of the later patent was filed Apr. 24, 1978, which matured into U.S. Pat. No. Re. 29,921 issuing on Feb. 22, 1979 and a divisional application, Ser. No. 773618, filed Mar. 2, 1977, which matured into U.S. Pat. No. 4,123,785 issuing on Oct. 31, 1978, both being directed to a recorder for cardiac signals. A much improved recorder is described in application Ser. No. 918,698 filed June 23, 1978, and issuing as U.S. Pat. No. 4,211,238, on July 8, 1980, for "Recorder for Ambulatory Monitoring of Electrical Signals," by Shu and Squires. A new method for marking and enhancing CRT screens showing abnormal ECG beats is described in Wong U.S. Pat. No. 4,625,278 issued Nov. 25, 1986.